The invention relates to the field of x-ray inspection systems, and in particular to an x-ray inspection system for automatically detecting nuclear weapons materials within an object under inspection.
The detection of contraband (e.g., explosives and drugs) in closed containers is of growing importance worldwide. World events have necessitated tighter screening requirements for the contents of containers placed on aircraft to detect the presence of explosives. In addition, to combat the illegal flow of narcotics across national borders, the contents of containers, such as loaded trucks and vehicles must be inspected to check for the presence of narcotics. High energy x-ray inspection systems remain one of the only technologies capable of inspecting loaded cargo containers and vehicles.
There is also a need to inspect containers for nuclear grade weapons"" materials. There is a growing concern that some of these materials may come into possession of terrorists, due to the relatively large volume of nuclear weapons grade materials stored worldwide. Detectors such as Geiger counters and gamma ray detectors are well known for detecting nuclear weapons materials. However, since Uranium does not emit a significant flux of gamma rays, it can not be detected by a gamma ray detector (e.g., a gamma ray detector mounted outside of the truck which contains the contraband). Therefore, there is a need for an x-ray inspection systems capable of automatically detecting the presence of nuclear weapons materials.
An object of the present invention is to automatically detect nuclear weapons materials using an x-ray inspection system.
Briefly, according to the present invention, an x-ray inspection system generates a high energy x-ray beam that traverses an object under inspection. A detector detects x-ray energy from the object and provides a detected signal indicative thereof. The detected signal is processed to detect the presence of an area of very high x-ray attenuation within the object under inspection, which is indicative of nuclear weapons materials, wherein the x-ray absorption of the nuclear weapons material is much greater than all of the elements of atomic number approximately equal to or lower than iron.
The high energy x-ray beam may be a fan beam or a pencil beam. In a fan beam embodiment, the detector is a transmission detector.
Because of the high atomic number (Z) and high density of nuclear weapons materials Uranium and Plutonium, both of these materials attenuate (i.e., either scatter out of the beam or absorb) incident x-rays significantly more than ordinary materials. In addition, very high Z materials such as nuclear weapons materials (e.g., Uranium and Plutonium), as well as lead, produce no scattered x-rays which are able to penetrate outside of their block of material because the scattered x-rays are self absorbed within the very high Z materials. Therefore, these materials can be detected by a single transmission detector, and, in addition, if the x-ray system forms a pencil beam, by noting that the detectors which monitor the scattered radiation give no signal for the region in question.
Advantageously, the inspection system of the present invention automatically detects the presence of nuclear weapons materials. In addition, the system may also operate to detect other contraband (e.g., drugs and explosives) in addition to nuclear weapons materials.
These and other objects, features and advantages of the present invention will become apparent in light of the following detailed description of preferred embodiments thereof, as illustrated in the accompanying drawings.